1. Field of the Invention
The invention relates to a grinding machine in which a plurality of grinding wheels are mounted on a swivel slide.
2. Discussion of Background
In an existing art, there are disclosed various grinding machines that are able to perform various types of grinding on a workpiece by turning a swivel slide having a plurality of grinding wheels. For example, Japanese Patent Application Publication No. 2009-095911 (JP-A-2009-095911) describes a grinding machine in which grinding wheels are arranged at front and rear sides of a swivel slide and the grinding wheels are arranged so that the direction of reactive force that occurs during machining is directed toward the center of a turning axis. In addition, Japanese Patent Application Publication No. 2009-101480 (JP-A-2009-101480) describes a grinding machine in which grinding wheels are arranged at front and rear sides of a swivel slide and the positions of the grinding wheel shafts are lowered to thereby make it possible to further improve stiffness. In addition, Japanese Patent Application Publication No. 54-295 (JP-A-54-295) describes a grinding machine that has two types of straight grinding wheels, that is, a straight grinding wheel that grinds a journal portion of a crankshaft and a straight grinding wheel that grinds a pin portion of the crankshaft, arranged on a swivel slide and that has a structure for changing the grinding wheels by turning the swivel slide 180 degrees.
In the existing techniques described in JP-A-2009-095911 and JP-A-2009-101480, the swivel slide is turned by a direct drive motor, the swivel slide has a rotor and a stator inside, and, furthermore, the grinding wheels are provided at the front and rear sides of the swivel slide. For this reason, the swivel slide is thick, the size of the swivel slide is large when regarded as a casing, and the weight of the swivel slide is also heavy. Thus, the size of a drive motor that moves the swivel slide toward or away from a workpiece also increases, so that the size of the grinding machine increases. In addition, the grinding wheels are provided on the side surfaces of the swivel slide, so that the position of each swivel slide cannot be adjusted in a direction to approach the turning axis. In addition, when the swivel slide is turned in order to change the grinding wheels for grinding a workpiece, it takes time to turn the swivel slide a having large size and a heavy weight. This elongates the machining time.
When the swivel slide is formed in a plate-like shape and then grinding wheels are arranged on the swivel slide in order to reduce the size and weight of the swivel slide, it is possible to reduce the apparent size and weight of the swivel slide, and the flexibility of arrangement of the grinding wheels increases. However, it is necessary to arrange a drive motor, such as a servo motor, for turning the swivel slide so as to protrude upward from the swivel slide as in the case of JP-A-54-295. A ball screw, or the like, for moving the swivel slide forward or backward is arranged below the swivel slide, and it is considerably difficult to arrange a turning drive motor below the swivel slide, so that not only the height increases but also grinding wheels must be arranged around the turning drive motor. Furthermore, unless the plurality of grinding wheels are arranged at appropriate positions, after turning the swivel slide in order to change the grinding wheel that grinds a workpiece, a relative displacement between the swivel slide and the workpiece increases to thereby elongate the machining time. However, in the existing art, the arrangement of the grinding wheels is determined in consideration only of the balance as the swivel slide and interference with a headstock or a workpiece during turning.